Hybrid structure for a surface acoustic wave device

ABSTRACT

A hybrid structure for a surface acoustic wave device comprises a useful layer of piezoelectric material having a free first surface and a second surface disposed on a support substrate that has a lower coefficient of thermal expansion than that of the useful layer. The hybrid structure further comprises a trapping layer disposed between the useful layer and the support substrate, and at least one functional interface of predetermined roughness between the useful layer and the trapping layer.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a national phase entry under 35 U.S.C. § 371 ofInternational Patent Application PCT/FR2017/051701, filed Jun. 26, 2017,designating the United States of America and published as InternationalPatent Publication WO 2018/002504 A1 on Jan. 4, 2018, which claims thebenefit under Article 8 of the Patent Cooperation Treaty to FrenchPatent Application Serial No. 1656191, filed Jun. 30, 2016.

TECHNICAL FIELD

This disclosure relates to the field of surface acoustic wave devices.It relates, in particular, to a hybrid structure adapted for themanufacturing of surface acoustic wave devices and to a manufacturingmethod of the hybrid structure.

BACKGROUND

Surface Acoustic Wave devices (SAW) use one or more inter-digitaltransducers developed on a piezoelectric substrate to convert electricalsignals into acoustic waves and vice versa. Such SAW devices orresonators are often used in filtering applications. Radio Frequency(RF) SAW technology on a piezoelectric substrate provides excellentperformances such as high-insulation and low-insertion losses. For thisreason, it is used for RF duplexers in wireless communicationapplications. Nevertheless, in order to be more competitive with RFduplexers based on Bulk Acoustic Wave (BAW) technology, RF SAW devicesrequire that the temperature stability of their frequency response beimproved.

The operating frequency dependence of the SAW devices according to thetemperature, or the thermal coefficient of frequency (TCF), depends, onthe one hand, on variations in the spacing between the interdigitalelectrodes of the transducers, which are generally due to the relativelyhigh coefficient of thermal expansion (CTE) of the piezoelectricsubstrates used. On the other hand, the TCF depends on the coefficientof thermal velocity because the expansion or contraction of thepiezoelectric substrate is accompanied by an increase or decrease in thevelocity of the surface acoustic wave. To minimize the thermalcoefficient of frequency (TCF), an aim is, therefore, to minimize theexpansion/contraction of the piezoelectric substrate, especially in thesurface zone in which the acoustic waves will propagate.

The article by K. Hashimoto, M. Kadota et al., “Recent development oftemperature compensated SAW devices,” IEEE Ultrasonic. Symp. 2011, pages79-86, 2011, provides an overview of the approaches commonly used toovercome the temperature dependency problem of the frequency response ofSAW devices.

One approach is to use a hybrid substrate, for example, composed of alayer of piezoelectric material arranged on a silicon substrate. The lowCTE of the silicon makes it possible to limit the expansion/contractionof the piezoelectric layer according to temperatures. In the case of apiezoelectric layer of lithium tantalate (LiTaO₃), the article indicatesthat a ratio of 10 between the thickness of LiTaO₃ and the thickness ofthe silicon substrate makes it possible to adequately improve thethermal coefficient of frequency (TCF).

The document DE102004045181 also discloses a structure suitable for SAWapplications, comprising a piezoelectric layer arranged on acompensating layer (for example, silicon).

One of the disadvantages of such a hybrid substrate comes from thepresence of interfering acoustic waves (as called “spurious acousticmodes” in the article “Characterization of bonded wafer for RF filterswith reduced TCF,” B. P. Abbott et al., Proc. 2005 IEEE InternationalUltrasonics Symposium, Sept. 19-21, 2005, pp. 926-929), which negativelyimpact the frequency characteristics of the resonator arranged on thehybrid substrate. These interfering resonances are, in particular,related to interfering reflections on the underlying interfaces,especially the interface between the LiTaO₃ and the silicon. Onesolution to reduce these interfering resonances is to increase thethickness of the LiTaO₃ layer. This is supposed to also increase thethickness of the silicon substrate in order to retain the TCFimprovements; the total thickness of the hybrid substrate is then nolonger compatible with the thickness reduction needs of the finalcomponents, especially on the cellphone market. Another solutionproposed by K. Hashimoto is to roughen the lower surface of the LiTaO₃layer so as to limit the acoustic wave reflections on the LiTaO₃ layer.Such roughening presents a handling difficulty when a direct bondingprocess, requiring very smooth surfaces to be assembled, is used for themanufacturing of the hybrid substrate.

Another disadvantage of a hybrid substrate according to the prior artstems from the presence of the support of semiconductor siliconmaterial, which even if it is highly resistive, is capable of containingfree charge carriers and of impacting the performance of the device,especially by increasing the insertion losses and the distortions(linearity) of the RF signal with respect to a solid piezoelectricsubstrate.

To improve the performance of radiofrequency devices, the documentWO2016/087728 proposes a structure comprising a trapping layercharacterized by a density of specific defects, arranged on the supportsubstrate.

BRIEF SUMMARY

A purpose of the present disclosure is to remedy some or all of thedisadvantages of the prior art. An aim of the disclosure is to propose ahybrid structure enabling the reduction and/or elimination of theinterfering acoustic waves and ensuring a stable performance for devicesoperating at high frequencies.

The present disclosure relates to a hybrid structure for surfaceacoustic wave device comprising a useful layer of piezoelectric materialhaving a first face free and a second face placed on a carrier substratewhose coefficient of thermal expansion is lower than that of the usefullayer, the hybrid structure being characterized in that it comprises:

-   -   a trapping layer interposed between the useful layer and the        carrier substrate;    -   at least one functional interface of determined roughness        between the useful layer and the trapping layer.

The trapping layer of the hybrid structure according to this disclosureeffectively traps the potentially generated moving electric loads in thecarrier substrate while operating the developed RF SAW device on thehybrid structure. The RF performances (linearity, insertion losses) thusreach a good level, comparable or even superior to that of technologieson large piezoelectric substrates.

The determined roughness functional interface allows efficient diffusionof the acoustic waves capable of propagating in depth in the usefullayer, thus avoiding their interfering reflections, which are known tonegatively impact the signal quality of the SAW device. This diffusionof the acoustic waves is rendered more efficient by the fact that thefunctional interface is located between the useful layer and thetrapping layer. Indeed, in addition to its trapping qualities of movingloads, the trapping layer makes it possible to efficiently screen theunderlying interface with the carrier substrate, the interfacecontributing in the hybrid structures to reflect acoustic waves.

According to advantageous features of the disclosure, taken alone orcombined:

-   -   the trapping layer is directly in contact with the carrier        substrate;    -   the trapping layer is formed of a material selected from among        amorphous silicon, polycrystalline silicon, amorphous or        polycrystalline germanium;    -   the trapping layer is formed by implantation of atomic species        in a surface layer of the carrier substrate or by etching and        structuring of the surface layer of the carrier substrate;    -   the determined roughness of the functional interface has a        peak-to-valley amplitude greater than 0.3 micron, advantageously        greater than or equal to 0.5 micron, or even 1 micron;    -   the functional interface is formed by the interface between the        useful layer and the trapping layer, the second face of the        useful layer having the determined roughness;    -   the functional interface is formed by the interface between a        first interlayer arranged on the second face of the useful layer        and the trapping layer; the trapping layer having the determined        roughness;    -   the first interlayer comprises a material selected from among        silicon oxide, silicon nitride, silicon oxynitride, or a        material of the same type as the one forming the useful layer;    -   the hybrid structure comprises a second functional interface;    -   the second functional interface is formed by the interface        between the useful layer and a second interlayer arranged on the        first interlayer, the second functional interface having a        second determined roughness with a peak-to-valley amplitude        greater than 0.1 micron;    -   the second interlayer comprises a material selected from among        silicon oxide, silicon nitride, silicon oxynitride, or a        material of the same type as the one forming the useful layer;    -   the first interlayer and the second interlayer are formed of the        same material;    -   the useful layer comprises a piezoelectric material selected        from among lithium tantalate (LiTaO₃), lithium niobate (LiNbO₃),        quartz, zinc oxide (ZnO),or aluminum nitride (AlN);    -   the carrier substrate is a solid substrate or a composite        substrate comprising at least one blank layer or comprising all        or part of microelectronic components.

The present disclosure also relates to a surface acoustic wave devicecomprising a hybrid structure such as above.

The present disclosure further relates to a manufacturing method of ahybrid structure for a surface acoustic wave device comprising:

-   -   a step of providing a useful layer of piezoelectric material        comprising a first face and a second face having a determined        roughness;    -   a step of providing a carrier substrate having a coefficient of        thermal expansion lower than the useful layer;    -   an assembly step for arranging the useful layer on the carrier        substrate;

wherein, the method further comprises, prior to the assembly step, aforming step of a trapping layer on the second face of the useful layer,the interface between the trapping layer and the useful layer forming afunctional interface of determined roughness, the assembling step beingcarried out between the trapping layer and the carrier substrate.

The present disclosure also relates to another manufacturing method of ahybrid structure for a surface acoustic wave device comprising:

-   -   a step of providing a useful layer of piezoelectric material        comprising a first face and a second face;    -   a step of providing a carrier substrate having a coefficient of        thermal expansion lower than the useful layer;    -   an assembly step for arranging the useful layer on the carrier        substrate;

wherein, the method further comprises, prior to the assembly step:

-   -   a forming step of a trapping layer having a determined roughness        on the carrier substrate;    -   a forming step of a first interlayer on the trapping layer, the        interface between the trapping layer and the first interlayer        forming a functional interface of determined roughness.

According to advantageous features of this manufacturing method, takenalone or combined:

-   -   the determined roughness of the functional interface has a        peak-to-valley amplitude greater than 0.3 micron, advantageously        greater than or equal to 0.5 micron, or even 1 micron;    -   the assembly step takes place between the first interlayer and        the second face of the useful layer;    -   the manufacturing method of a hybrid structure comprises, prior        to the assembly step, a forming step of a second interlayer on        the second face of the useful layer having a second determined        roughness, the assembling step being carried out between the        first interlayer and the second interlayer; the interface        between the useful layer and the second interlayer forming a        second functional interface.

BRIEF DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the disclosure will emerge fromthe detailed description that follows, with reference to theaccompanying drawings in which:

FIGS. 1 to 3 show hybrid structures according to the disclosure;

FIG. 4 shows a surface acoustic wave device according to the disclosure;

FIGS. 5A-5E, 6A-6E, and 7A-7E show manufacturing methods of hybridstructures according to the disclosure.

DETAILED DESCRIPTION

In the descriptive part, the same references in the figures may be usedfor elements of the same type.

The figures are schematic representations that, for the sake of clarity,are not to scale. Especially, the thicknesses of the layers along the zaxis are not to scale with respect to the lateral dimensions along the xand y axes.

As illustrated in FIG. 1, a hybrid structure 100 for a surface acousticwave device comprises a useful layer 10 of piezoelectric material havinga free first face 1 and a second face 2. The useful layer 10 comprises apiezoelectric material selected from among, for example, lithiumtantalate (LiTaO₃), lithium niobate (LiNbO₃), quartz, zinc oxide (ZnO),or aluminum nitride (AlN).

The useful layer 10 is arranged on a carrier substrate 20 whosecoefficient of thermal expansion is lower than that of the useful layer10. The carrier substrate 20 is, for example, formed of silicon orgermanium.

The hybrid structure 100 according to the disclosure also comprises atrapping layer 30 interposed between the useful layer 10 and the carriersubstrate 20. The term “trapping layer” is understood to mean a layercapable of trapping the moving electric loads likely to be present inthe carrier substrate 20. By way of example, the trapping layer 30 isformed of a material chosen among amorphous silicon, polycrystallinesilicon, amorphous or polycrystalline germanium. The trapping layer 30may also be formed by a technique or combination of techniquesincluding:

-   -   the ion implantation into a surface layer of the carrier        substrate 20; for a silicon substrate, an implantation of, for        example, argon, silicon or nitrogen ions may be carried out in        order to generate a perturbed surface layer capable of trapping        moving loads originating from the carrier substrate 20;    -   or by etching and structuring a surface layer of the carrier        substrate 20, for example, by mechanical, wet, or dry chemical        etching, inducing a structuring of the surface, a preferred        trapping site for moving loads originating from the carrier        substrate 20.

The thickness of the trapping layer 30 may be between a few tens ofnanometers and a few microns, or even a few tens of microns.

Advantageously, the trapping layer 30 is directly in contact with thecarrier substrate 20, which allows for efficient trapping of the movingloads, generated in the carrier substrate 20.

The hybrid structure 100 according to the disclosure also comprises atleast one functional interface 31 of determined roughness between theuseful layer 10 and the trapping layer 30. The roughness of thefunctional interface 31 is defined by the maximum peak-to-valleyamplitude, measured, for example, by mechanical or optical profilometryon measure profiles of about 50 microns to 500 microns or measuresurfaces of about 50×50 μm² to 500×500 μm². Advantageously, thepeak-to-valley determined roughness is greater than 0.3 micron.Advantageously, it is even greater than or equal to 0.5 micron, or even1 micron. It is preferably between 0.3 micron and 5 microns.

Also advantageously, the spectral density (PSD) of the roughness of thefunctional interface 31 covers all or part of the spectral band ofwavelengths of the interfering waves, which are desired to beeliminated. Preferably, the determined roughness has spatial wavelengthsand an amplitude at least equal to a quarter of the interferingwavelengths.

The determined roughness of the functional interface 31 can, therefore,be adapted in amplitude and potentially in spectral density depending onthe frequency of the acoustic waves of the SAW device, which will bemanufactured on the hybrid structure 100, for its ability to efficientlydiffuse the acoustic waves susceptible to spread in the useful layer 10.

The trapping layer 30 of the hybrid structure 100 according to thedisclosure effectively traps the potentially generated moving electricloads in the carrier substrate 20 during operation of the RF SAW devicedeveloped on the first face 1 of the hybrid structure 100. The RFperformances (linearity, insertion losses) thus reach a very good level,comparable or even superior to that of the technologies on massivepiezoelectric substrates.

The functional interface 31 of determined roughness enables efficientdiffusion of the acoustic waves capable of spreading in depth in theuseful layer 10, thus avoiding their interfering reflections, which areknown to negatively impact the signal quality of the SAW device.

According to a first embodiment, illustrated in FIG. 1, the functionalinterface 31 is formed by the interface between the useful layer 10 andthe trapping layer 30.

According to a second embodiment, illustrated in FIG. 2, the functionalinterface 31 is formed by the interface between a first interlayer 40arranged on the second face 2 of the useful layer 10 and the trappinglayer 30. By way of example, the first interlayer 40 may comprise amaterial chosen among silicon oxide, silicon nitride, silicon oxynitrideor a material of the same type as the useful layer.

These two embodiments are advantageous in that the trapping layer 30makes it possible to keep away and to screen the underlying interfacewith the carrier substrate 20, the latter being a strong contributor, inthe usual hybrid structures, to the reflection of the acoustic wavesspreading in the volume of the useful layer 10. The interface with thecarrier substrate 20 is screened in the sense that the majority, if notall, of the acoustic waves reaching the functional interface 31 will beefficiently diffused by the latter and thus never reach that interface.

According to a third embodiment, illustrated in FIG. 3, the hybridstructure 100 comprises a second functional interface 32 having a seconddetermined roughness, whose peak-to-valley amplitude is greater than 0.1micron. It is preferably between 0.1 micron and 5 microns. It will benoted that the second functional interface 32 may have a seconddetermined roughness different from the determined roughness of thefirst functional interface 31, both in amplitude and in spectraldensity. Advantageously, the spectral densities may be chosen to coverin a complementary manner the spectral band of wavelengths of theinterfering waves, which are desired to be eliminated.

The second functional interface 32 is formed by the interface betweenthe useful layer 10 and a second interlayer 50 arranged on the firstinterlayer 40. By way of example, the second interlayer 50 comprises amaterial chosen among silicon oxide, silicon nitride, and siliconoxynitride. The second interlayer 50 may also comprise a material of thesame type as that constituting the useful layer 10. For a useful layer10 made of LiTaO₃, the second interlayer 50 may, for example, consist ofa deposited amorphous LiTaO₃ layer.

According to an advantageous variant of this third embodiment, the firstinterlayer 40 and the second interlayer 50 are formed of the samematerial; thus, the interface between these two layers contributeslittle or nothing to interfering reflections, due to the absence of anydifference in acoustic impedance between the two layers.

In the various embodiments described, the carrier substrate is a bulksubstrate. Alternatively, it may consist of a composite substratecomprising at least one blank layer or a structured layer, comprisingall or part of microelectronic components. These configurations areparticularly advantageous for producing co-integrated systems, includingsurface acoustic wave devices in and on the useful layer 10, andcomponents (switches, amplifiers, other filters, etc.) in the carriersubstrate.

The disclosure also relates to a surface acoustic wave device 200comprising a hybrid structure 100, illustrated in FIG. 4. The device 200comprises, for example, interdigital metal electrodes 201 on the firstface 1 of the useful layer 10, between which spread the acoustic waves.

The hybrid structure 100 is particularly suitable for the manufacturingof surface acoustic wave devices 200 using acoustic wave frequenciesranging from 700 MHz to 3 GHz.

The disclosure also relates to a manufacturing method of a hybridstructure 100 for a surface acoustic wave device 200, which will bedescribed with reference to FIGS. 5A to 7E.

The manufacturing method first comprises a step of providing a usefullayer 10 of piezoelectric material comprising a first face 1 and asecond face 2 having a determined roughness. The roughness is defined bythe peak-to-valley maximum amplitude, measured, for example, bymechanical or optical profilometry, on measurement profiles of about 50to 500 microns or measuring surfaces of about 50×50 μm² to 500×500 μm₂.Advantageously, the determined roughness is greater than 0.3 micron,even greater than or equal to 0.5 micron, or even greater than 1 micron.Preferably, it is even between 0.3 micron and 5 microns.

Also advantageously, the spectral density of the roughness of thefunctional interface 31 covers all or part of the spectral band ofwavelengths of the interfering waves, which are desired to beeliminated. Preferably, the determined roughness has spatial wavelengthsand an amplitude at least equal to a quarter of the interferingwavelengths.

The determined roughness of the functional interface 31 can, therefore,be adapted in amplitude and potentially in spectral density depending onthe frequency of the acoustic waves of the SAW device that will bemanufactured on the hybrid structure 100 for its ability to effectivelydiffuse the acoustic waves susceptible to spread in the useful layer 10.

The determined roughness can be achieved on the second face 2 bymechanical lapping techniques, chemical-mechanical polishing, wet or drychemical etching, or a combination of these various techniques. The aimis to create on the second face 2 of the useful layer 10 a uniformroughness of determined amplitude over the whole face. By way ofexample, such a roughness can be obtained by the typical treatments ofthe roughened rear faces of the wafers (lithium tantalate, lithiumniobate, etc.) used in the semiconductor industry.

As previously stated and without it being limiting, the useful layer 10comprises a piezoelectric material selected from among lithium tantalate(LiTaO₃), lithium niobate (LiNbO₃), quartz, zinc oxide (ZnO), oraluminum nitride (AlN).

According to an advantageous embodiment, the useful layer 10 is includedin a donor substrate 11, having a second face 2 of determined roughnessand a first face 1′ (FIG. 5A).

The manufacturing method according to the disclosure also comprises aforming step of a trapping layer 30 on the second face 2 of the usefullayer 10 or of the donor substrate 11 (FIG. 5B). The interface betweenthe trapping layer 30 and the useful layer 10 (or the donor substrate11) forms a functional interface 31 of determined roughness.Advantageously, the trapping layer 30 is formed of a material chosenamong amorphous silicon, polycrystalline silicon, amorphous orpolycrystalline germanium. The trapping layer 30 can be prepared byknown chemical deposition techniques (PECVD, LPCVD, etc.).

The trapping layer 30 typically has a thickness of between a few tens ofnanometers and a few microns, or even a few tens of microns.

Advantageously, the forming step of the trapping layer 30 comprises astep of smoothing the free surface of the trapping layer 30, consisting,for example, of chemical mechanical polishing, smoothing plasma etchingor wet chemical etching. Preferably, the free surface of the trappinglayer 30 will have a low roughness (typically<0.5 nm RMS, measured byatomic force microscopy) and good flatness, for the purpose of asubsequent assembly step.

The manufacturing method also includes a step of providing a carriersubstrate 20 (FIG. 5C) having a coefficient of thermal expansion lowerthan that of the useful layer 10. Advantageously, the carrier substrate20 is made of silicon, this material being widely available andcompatible with the semiconductor industry. Alternatively, it may alsobe made of germanium or other materials compatible with the subsequentsteps of the method and the preparation of the surface acoustic wavedevice.

The manufacturing method then comprises an assembly step for arrangingthe donor substrate 11 (or the useful layer 10) on the carrier substrate20 (FIG. 5D). The assembly step takes place between the trapping layer30 and the carrier substrate 20, so the surface properties of thetrapping layer 30 and of the carrier substrate 20 must be properlycontrolled. Advantageously, the assembly step comprises direct bondingby molecular adhesion. This molecular adhesion bonding technique ispreferred in that it does not require the use of a layer of additionalmaterial.

Alternatively, the assembly step may include adhesive bonding, metalbonding, anodic bonding, or any other type of bonding known from thestate of the art and compatible with the intended utilization.

Advantageously, the assembly step comprises, prior to bonding, acleaning sequence to ensure a good level of cleanliness (removal ofparticles, hydrocarbon and metal contaminants, etc.) from the surfacesbefore bonding.

According to a variant of the method, a layer of the same type as thetrapping layer 30 may be arranged on the carrier substrate 20 prior tothe assembly step and will be prepared in order to be bonded to thetrapping layer 30. Indeed, depending on the type of the trapping layer30 and that of the carrier substrate 20, it may be advantageous,especially in the case of direct bonding by molecular adhesion, to forma bonding interface between two materials of the same type.

To consolidate the bonding interface, the bonded hybrid structure 101can be subjected to a heat treatment. It should be noted that thematerials of the donor substrate 11 (or of the useful layer 10) and ofthe carrier substrate 20 exhibit very different coefficients of thermalexpansion. The heat treatment applied must, therefore, remain at atemperature lower than the temperature of damage or breakage of thebonded hybrid structure 101. The temperature range is typically betweena few tens of degrees and 500° C.

In the case illustrated in FIGS. 5A to 5E, where the useful layer 10 isincluded in a donor substrate 11, the manufacturing process furthermorecomprises a step of thinning the donor substrate 11 (FIG. 5E) to formthe useful layer 10 and the first face 1, on which the surface acousticwave devices will be prepared.

This thinning step can be carried out using various known techniques ofthe prior art, in particular:

-   -   the SMART CUT® process, which is particularly suited to the        formation of very thin useful layers (typically of thickness        less than or equal to 1 micron): it is based on an implantation        of gaseous species in the donor substrate 11, at the level of        its second face 2, prior to the assembly step, to form a        weakened buried plane; after assembly, the donor substrate 11        will separate along the weakened plane, so as to leave integral        with the carrier substrate 20 only the useful layer 10.    -   chemical-mechanical thinning processes, including mechanical        lapping, chemical-mechanical polishing and chemical etching,        suitable for the formation of useful layers of thicknesses        ranging from a few microns to a few tens, or even hundreds of        microns.

At the end of this manufacturing process, a hybrid structure 100according to the disclosure is obtained (FIG. 5E).

The disclosure relates to another manufacturing method of a hybridstructure 100 for a surface acoustic wave device, first comprising astep of providing a useful layer 10 of piezoelectric material comprisinga first face 1 and a second face 2.

As stated above and without limitation, the useful layer 10 comprises apiezoelectric material selected from among lithium tantalate (LiTaO₃),lithium niobate (LiNbO₃), quartz, zinc oxide (ZnO), or aluminum nitride(AlN).

According to an advantageous embodiment, the useful layer 10 is includedin a donor substrate 11 having a second face 2 and a first face 1′ (FIG.6A).

The manufacturing method also comprises a step of providing a carriersubstrate 20 having a coefficient of thermal expansion lower than theuseful layer 10. Advantageously, the carrier substrate 20 is made ofsilicon, the material being widely available and compatible with thesemiconductor industry. As mentioned above, it may alternatively beformed or comprise germanium or other materials compatible with thesubsequent manufacturing steps.

The manufacturing method also comprises a forming step of a trappinglayer 30 on the carrier substrate 20 (FIG. 6B). The trapping layer 30has a predetermined roughness.

Advantageously, the trapping layer 30 is formed of a material selectedfrom among amorphous silicon, polycrystalline silicon, amorphous orpolycrystalline germanium. It can be prepared by known techniques ofchemical deposition (CVD).

The trapping layer 30 may also be formed by a technique or combinationof techniques including:

-   -   the ion implantation in a surface layer of the carrier substrate        20; for a silicon substrate, an implantation, for example, of        argon ions, silicon, nitrogen, etc., may be carried out to        generate a disturbed surface layer capable of trapping moving        loads from the carrier substrate 20;    -   or by etching and structuring a surface layer of the carrier        substrate 20; for example, by mechanical etching, wet or dry        chemical, inducing a structuring of the surface, a trapping        privileged site for moving loads from the carrier substrate 20.

The trapping layer 30 may have a thickness ranging from a few tens ofnanometers to several microns or tens of microns.

The roughness of the free surface of the trapping layer 30, after itsformation on the carrier substrate 20, is defined by the maximumpeak-to-valley amplitude, measured, for example, by mechanical oroptical profilometry on measure profiles of about 50 microns to 500microns or measure surfaces of about 50×50 μm² to 500×500 μm₂.Advantageously, the determined roughness is greater than 0.3 micron, oreven greater than or equal to 0.5 micron, or even greater than or equalto 1 micron. It is preferably between 0.3 micron and 5 microns.

Also advantageously, the spectral density of the roughness of thefunctional interface 31 covers all or part of the spectral band ofwavelengths of the interfering waves, which are desired to beeliminated. Preferably, the determined roughness has spatial wavelengthsand an amplitude at least equal to a quarter of the interferingwavelengths.

The determined roughness can be obtained on the free surface of thetrapping layer 30, either directly after deposition of the layer, or bymechanical lapping techniques, chemical-mechanical polishing, wet or drychemical etching, or a combination of these techniques. The aim is tocreate on the free surface of the trapping layer 30 a uniform roughnessof determined amplitude. By way of example, such roughness may beobtained by “acid etch” type treatments or “alkali etch” made for thetreatment of roughened rear faces of the silicon wafers used in thesemiconductor industry. According to another example, the determinedroughness of the free surface of the trapping layer 30 may be obtainedby mechanical lapping (typically with a diamond wheel of grain 2000) andwet chemical etching (typically by TMAH) of the surface of the carriersubstrate 20 before depositing a trapping layer 30 in polycrystallinesilicon; the free surface of the trapping layer 30 after deposition onthe carrier substrate 20 has then the determined roughness of about 0.5microns peak-to-valley (FIG. 6B′).

The manufacturing method then comprises a forming step of a firstinterlayer 40 on the trapping layer 30. The interface between thetrapping layer 30 and the first interlayer 40 forms the functionalinterface 31 of determined roughness. The first interlayer 40 maycomprise a material selected from among silicon oxide, silicon nitride,silicon oxynitride, or a material of the same type as the useful layer10. It may be prepared by chemical deposition. Advantageously, asmoothing step (for example, chemical-mechanical polishing) is carriedout on the free surface of the first interlayer 40, for the purpose ofthe subsequent assembly step on the donor substrate 11 (or the usefullayer 10). This option is particularly suitable when the subsequentassembly step includes bonding by molecular adhesion.

The first interlayer 40 may also comprise a polymeric material, whichmay, for example, be deposited by centrifugation. The advantage of thistype of material is that the smoothing can be carried out directlyduring the deposition. This option is particularly suitable when thesubsequent joining step comprises an adhesive bonding.

Finally, the manufacturing method comprises an assembly step forarranging the donor substrate 11 (or useful layer 10) on the supportingcarrier substrate 20. In particular, the assembly is carried out betweenthe first interlayer 40 and the second face 2 of the donor substrate 11(FIG. 6D).

Advantageously, the assembling step includes a direct bonding bymolecular adhesion. This molecular bonding technique is advantageous inthat it does not require the use of an additional material layer.Alternatively, the joining step may include adhesive bonding, metalbonding, anodic bonding, or any other kind of bonding known in the priorart and compatible with the intended application. Advantageously, theassembling step includes, prior to bonding, a cleaning sequence toensure a good level of cleanliness (removal of particles, hydrocarbonsand metal contaminants) to the surfaces before bonding.

To consolidate the bonding interface, the bonded hybrid structure 101may be subjected to a heat treatment, at low or medium temperature toprevent damage to the heterostructure, typically between several tens ofdegrees and 500° C.

In the instance, illustrated in FIGS. 6A to 6E, where the useful layer10 is included in a donor substrate 11, the manufacturing methodfurthermore comprises a thinning step of the donor substrate 11 (FIG.6E) to form the useful layer 10 and the first face 1, on which thesurface acoustic wave devices will be developed.

This thinning step can be made from various techniques known in theprior art, as previously discussed.

At the end of this manufacturing method, a hybrid structure 100according to the disclosure is obtained (FIG. 6E).

According to a variant of the above manufacturing method, illustrated inFIGS. 7A to 7E, the second face 2 of the useful layer 10 (or donorsubstrate 11, in the case where the useful layer 10 is included in adonor substrate) has a second determined roughness (FIG. 7A). Thepeak-to-valley amplitude of the second determined roughness isadvantageously greater than 0.1 micron.

This variant of the manufacturing method comprises a forming step of asecond interlayer 50 on the second face 2 of the useful layer 10 or thedonor substrate 11 as shown in FIG. 7B. The second interlayer 50 maycomprise a material or a stack of materials selected from among siliconoxide, silicon nitride, and silicon oxynitride. The second interlayer 50may also comprise a material of the same type as that forming the usefullayer 10 to limit the problems associated with differences in thermalexpansion.

The interface between the useful layer 10 and the second interlayer 50forms a second functional interface 32. Advantageously, the forming stepof the second interlayer 50 includes a step of smoothing its freesurface for the purpose of the assembly step.

Prior to the assembly step, the trapping layer 30 having a firstpredetermined roughness is formed on the carrier substrate 20. Then, thefirst interlayer 40 is formed on trapping layer 30 (FIG. 7C). Theinterface between these two layers forms the functional interface 31 ofdetermined roughness.

Optionally, the first 40 and second 50 interlayers may be composed ofthe same material.

This variant of the manufacturing method further comprises the assemblyof the first 40 and second 50 interlayers, advantageously by directbonding, but this is not to be taken in a limiting manner.

A heat treatment may optionally be carried out to consolidate thebonding interface of the bonded hybrid structure 101.

When the useful layer 10 is included in a donor substrate 11, a thinningstep, as already stated previously, is realized, leading to theobtaining of the hybrid structure 100 (FIG. 7E).

Of course, the disclosure is not limited to the described embodimentsand can be applied to alternative embodiments within the scope of theinvention as defined by the claims.

1-18. (canceled)
 19. A hybrid structure for a surface acoustic wavedevice, comprising: a useful layer of piezoelectric material having afirst face free and a second face; a carrier substrate having acoefficient of thermal expansion lower than a coefficient of thermalexpansion of the useful layer; a trapping layer interposed between theuseful layer and the carrier substrate; and at least one functionalinterface between the useful layer and the trapping layer, thefunctional interface having a determined roughness having apeak-to-valley amplitude greater than 0.3 micron.
 20. The hybridstructure of claim 19, wherein the trapping layer is in direct physicalcontact with the carrier substrate.
 21. The hybrid structure of claim19, wherein the trapping layer comprises a material selected from thegroup consisting of amorphous silicon, polycrystalline silicon,amorphous and polycrystalline germanium.
 22. The hybrid structure ofclaim 19, wherein the trapping layer is formed by implantation of atomicspecies in a surface layer of the carrier substrate or by etching andstructuring of the surface layer of the carrier substrate.
 23. Thehybrid structure of claim 19, wherein the at least one functionalinterface comprises an interface between the useful layer and thetrapping layer, the second face of the useful layer having thedetermined roughness.
 24. The hybrid structure of claim 19, furthercomprising a first interlayer between the second face of the usefullayer and the trapping layer, and wherein the at least one functionalinterface comprises an interface between the first interlayer and thetrapping layer, a surface of the trapping layer having the determinedroughness.
 25. The hybrid structure of claim 24, wherein the firstinterlayer comprises a material selected the group consisting of siliconoxide, silicon nitride, silicon oxynitride, or a material of the usefullayer.
 26. The hybrid structure of claim 24, further comprising a secondfunctional interface.
 27. The hybrid structure of claim 26, furthercomprising a second interlayer on the first interlayer, and wherein thesecond functional interface comprises an interface between the usefullayer and the second interlayer, the second functional interface havinga second determined roughness whose peak-to-valley amplitude is greaterthan 0.1 micron.
 28. The hybrid structure of claim 27, wherein thesecond interlayer comprises a material selected from the groupconsisting of silicon oxide, silicon nitride, silicon oxynitride or amaterial of the useful layer.
 29. The hybrid structure of claim 27,wherein the first interlayer and the second interlayer are formed of thesame material.
 30. The hybrid structure of claim 19, wherein the usefullayer comprises a piezoelectric material selected from the groupconsisting of lithium tantalate (LiTaO₃), lithium niobate (LiNbO₃),quartz, zinc oxide (ZnO), and aluminum nitride (AlN).
 31. The hybridstructure of claim 19, wherein the carrier substrate is a bulksubstrate, a composite substrate comprising at least one blank layer, ora substrate comprising at least a portion of microelectronic components.32. A surface acoustic wave device comprising a hybrid structureaccording to claim
 19. 33. A method of manufacturing a hybrid structurefor a surface acoustic wave device, comprising: providing a useful layerof piezoelectric material having a first face, and a second face havinga determined roughness; forming a trapping layer on the second face ofthe useful layer, an interface between the trapping layer and the usefullayer forming a functional interface of determined roughness having apeak-to-valley amplitude greater than 0.3 micron; providing a carriersubstrate having a coefficient of thermal expansion lower than theuseful layer; and assembling the useful layer on the carrier substratewith the trapping layer between the useful layer and the carriersubstrate.
 34. A method of manufacturing a hybrid structure for asurface acoustic wave device, comprising: providing a useful layer ofpiezoelectric material having a first face and a second face; providinga carrier substrate having a coefficient of thermal expansion lower thanthe useful layer; forming a trapping layer having a determined roughnesson the carrier substrate; forming a first interlayer on the trappinglayer, an interface between the trapping layer and the first interlayerforming a functional interface having a determined roughness; andassembling the useful layer on the carrier substrate with the trappinglayer and the first interlayer between the useful layer and the carriersubstrate.
 35. The method of claim 34, wherein assembling the usefullayer on the carrier substrate comprises bonding the first interlayer tothe second face of the useful layer.
 36. The method of claim 34, furthercomprising, prior to assembling the useful layer on the carriersubstrate, forming a second interlayer on the second face of the usefullayer, the second interlayer having a surface having a second determinedroughness, and wherein assembling the useful layer on the carriersubstrate comprises bonding the first interlayer to the secondinterlayer, an interface between the useful layer and the secondinterlayer forming a second functional interface.